The present invention relates to a method of operating a bar code reader which is formed for the scanning and detection of bar codes.
Such bar code readers are for example used for the sorting of articles bearing the bar code, with sorting of the articles taking place as a result of an association of a respectively detected bar code to one of the articles. For example, in a luggage conveying system of an airport each article of luggage can be provided with a bar code which characterizes the airport at the destination. By detecting the destination airport stored in the bar code and by associating the corresponding bar code to the respective article of luggage it is possible to effect sorting into different dispatch departments automatically in the transport apparatus.
The correct association between a detected bar code and the object bearing this bar code is in this respect normally carried out as follows:
First of all, on entry of the object into a so-called reading field, a starting signal for an incremental transducer is generated by a light barrier, with the incremental transducer delivering incremental signals corresponding to the speed of transport of the object. In this manner the position of the object in the transport apparatus can be determined at any time from the incremental signal, with respect to a reference point formed for example by the start of the reading field.
If now a bar code is detected inside the scanning range by the bar code reader then the position of the bar code at its time of detection is determined and a check is made as to which object was located at this position at the time of detection.
The bar code is then associated to the object which is found during this investigation.
If the objects are exclusively arranged in series in the transport direction then it is sufficient to determine and evaluate the position in the transport direction in order to achieve a correct association. If objects can however also be arranged alongside one another then a corresponding evaluation of a position or component perpendicular to the transport direction is also necessary. The determination of the object positions can take place in this arrangement also by means other than the described incremental transducer. The incremental path signal can, in particular, be replaced by a timer interrupt of constant frequency when the conveying speed is constant.
Several parameters must be taken into account in this arrangement in determining the position of the detected bar code. On the one hand the spacing between the bar code reader and the detected bar code at the time of scanning must be found, which can for example take place by a transit time measurement. The position of the detected bar code can then be found from this scanning distance and also the position and the scanning angle of the bar code reader.
The scanning angles give information concerning the tilting of the bar code reader with respect to a Cartesian coordinate system which is advantageously so aligned that the x-axis extends in the transport direction of the object, the y-axis extends perpendicular to the transport direction in the plane of transport, which is normally horizontally aligned, and the z-axis extends perpendicular to the transport plane, i.e. is normally vertically aligned. The scanning angle a then specifies the angle of rotation of the bar code reader with respect to the x-direction, i.e. xcex1=0 when the scanning line extends in the x-direction. The scanning angle xcex2, also termed the skew angle, defines the tilting of the bar code reader in the x-direction, i.e. xcex2=0 when the bar code reader scans the objects vertically from above parallel to the z-axis. The scanning angle y defines a lateral tilting of the bar code reader about the x-axis, i.e. xcex3=0 with a scanning of the objects vertically from above.
The positions of the bar code reader and also of the detected bar code are advantageously set forth by coordinates of the quoted Cartesian coordinate system, i.e. by an x-coordinate, a y-coordinate and a z-coordinate.
Problematic in the association of the detected bar code to the respective objects is the fact that the position of the bar code reader in space is relatively complicated to determine. This position is normally determined during the installation of a corresponding bar code reading system, whereby the complexity of the installation work is significantly increased.
If the position of the bar code reader is subsequently changed with an already installed system, for example by rebuilding or other external influences, then the position of the bar code reader must be newly determined, which cannot normally be carried out by the operator of the bar code reading system himself. Accordingly, in this case a specially trained service technician must be used for the new adjustment of the system or the determination of the position of the bar code reader.
In addition to the position of the bar code reader the scanning angle must normally be newly determined with a new installation or with a later installation. The scaling of the incremental path transducer is not known in all cases so that this scaling must in some cases also first be determined on installation of a corresponding system.
It is an object of the invention to set out a method of operating a bar code reader with which the position of a bar code reader can be determined in a simple manner and largely automatically. Furthermore, it should also be possible to determine the scanning angle and the scaling of the incremental path transducer in a simple manner and as automatically as possible.
This object is satisfied in accordance with the invention by a method of operating a bar code reader in which one or more bar codes are detected at different positions within a scanning range of the bar code reader by the latter, the scanning distance between the bar code reader and the respectively detected bar code is found and the position and/or the scanning angle of the bar code reader is found from the respectively found scanning distance and from known position data of the detected bar code.
With the method of the invention the position and/or the scanning angle of the bar code reader can thus be found and stored in the bar code reader or in an evaluation circuit connected to the latter. The automatic finding of the position and/or the scanning angle of the bar code reader leads at least to a significantly simpler installation of a bar code reading system because the complicated manual determination of the position and/or the scanning angle of the bar code reader can be omitted.
The position of the bar code reader is in this arrangement advantageously determined as coordinates of a Cartesian coordinate system. If the bar codes are exclusively arranged lying one behind the other in the transport direction defined by the x-direction, then the determination of the x-coordinate is fundamentally sufficient for a correct association of the bar codes to the respective object.
Since the position and/or the scanning angle of the bar code reader was found using the described learning process of the invention, the normal operation, i.e. the scanning and association operation of the bar code reader, can be started, with the position and/or the scanning angles found in the learning process being used for the determination of the correct association.
In accordance with a preferred embodiment of the invention the position and/or the scanning angle of the bar code reader are found with respect to the scanning distances that are found and with respect to known relative positions of different bar codes relative to one another. For example, during the learning method, objects with a plurality of bar codes can be introduced into the scanning region of the bar code reader, with the geometrical positioning of the bar codes relative to one another being known. Thus the object can be for example be introduced into the scanning region such that two bar codes provided on the object have the same y- and z-coordinates and only have different x-coordinates, i.e. are only displaced relative to one another in the transport direction. When the spacing in the x-direction between the two bar codes is known, which represents the position of the bar codes relative to one another, then the x-coordinates of the bar code reader can be found after detection of the two bar codes by the bar code reader and the respective scanning distance found thereby.
It is basically possible for the objects with the bar code to be moved through the scanning regions so that the respective bar code is swept over by the scanning beam of the bar code reader during its transport movement. It is however also possible for the objects with the bar code to be introduced stationary into the scanning range so that the bar code can be swept over by the scanning beam in the stationary state. In this case the absolute position of the respective bar code can for example be directly determined, for example measured.
With a movement of the object bearing the bar code through the scanning range an incremental signal representative for the path traversed by the bar code is advantageously produced by an incremental path transducer coupled to the speed of movement, the actual incremental signal is in each case detected at the time of detecting a bar code, and the incremental transducer scale, i.e. the number of increments per traversed path, is respectively found from the known position data of the detected bar code and from the detected incremental signals.
If, for example, it is known that two bar codes arranged on an object are spaced 20 cm from one another in the x-direction then the difference from the two incremental transducer counts detected at the respective time of scanning of the bar codes can be formed and the scaling of the incremental path transducer, i.e. the number of increments per traversed path, can be found by forming the quotient of this difference and the known spacing.
By means of the scaling of the incremental path transducer the path traversed since starting the incremental transducer can then be found, for example also for each of the detected bar codes from the incremental signal found at the respective time of scanning, and this traversed path represents in each case the x-coordinate of the bar code at the time of scanning.
Further advantageous embodiments of the invention are set forth in the subordinate claims.